Livestock, particularly those confined to relatively small spaces, such as dairy cattle, require relatively frequent trimming or cutting of excess growth of the hooves. Prior art cutters or hoof nippers have a pair of opposing jaws provided with cutting blades which are moved toward and away from one another when the handles of the cutter are manually operated by a user. Animal hooves are relatively hard and a relatively large amount of force or high pressure must be exerted upon the cutting blades to accomplish the trimming of the hooves. Various lever linkages have been provided in the past to assist a person doing such trimming to exert the necessary force, but hand operated hoof cutters or hoof nippers still produce a great deal of stress on the hands and arms of the person doing the trimming. Even with strong persons having considerable experience, fatigue in the use of conventional hoof trimers or hoof nippers substantially limits the number of hooves which can be trimmed in any given session.
Another disadvantage of hoof nipper or hoof trimmers is that the cutting blades wear out relatively quickly and require frequent shapening. This wear results from abrasion in the form of sand and rocks which are picked up in the animal's hooves. Consequently, the blade closure must be capable of compensating for this wear and resharpening in order to prolong the life of the tool.
Typical hand-operated hoof trimmers or hoof nippers of the type commonly employed are disclosed in the patents to Baer U.S. Pat. No. 640,257; Stowell U.S. Pat. No. 1,066,675; and Uhlmann U.S. Pat. No. 4,130,938. In all of these patents, inter-engaging gears or toothed racks are provided between the handle and the opposed cutting blades to multiply the force obtained from squeezing the handle portions together. The mechanisms of these three patents differ somewhat from one another, but the underlying concept is the same. Even with this multiplication of force, however, such hoof cutters tire any person who is attempting to trim the hooves of a large number of animals in succession.
Three other patents directed to hoof trimming tools using rotating cutting blades are the patents to Krickel U.S. Pat. No. 1,000,821; Thomas U.S. Pat. No. 1,056,379; and Howe U.S. Pat. No. 2,523,368. The devices of these three patents are somewhat impractical since they are cumbersome to use. All of them require the animal's hoof to be in the same fixed position during the trimming operation. As a result, it is difficult for the operator to trim or cut at different angles, and also use the tool to scalp the pad of the hoof.
Power shears, pruning devices and the like have been provided to produce a relatively high pressure closure between a pair of opposed blades without requiring substantial amounts of squeezing force on the part of the user of such devices. Four patents of this type are the patents to Baird U.S. Pat. No. 492,931; Carter U.S. Pat. No. 693,231; Parhaniemi U.S. Pat. No. 3,138,869; and Lind U.S. Pat. No. 4,521,963. In Baird a threaded wedge is forced between the ends of two opposed pivoted lever arms for applying a highly multiplied force to the cutting blades of a bolt cutting machine. In another embodiment, a multiple point pivot arrangement is used instead of the wedge, with a pair of short lever arms engaging the ends of the longer lever arms which are attached to the bolt cutting head.
The Carter and Lind patents are directed to hydraulically operated bolt cutting devices and the Parhaniemi patent discloses a pruning device which uses either a hand-operated or electrically operated elongated rod to move a pair of interconnecting levers in a manner similar to the device of Baird. All of these patents employ interconnected levers and pivots in which elongated levers having the cutting blades at one end are pivotally connected to intermediate levers, the opposite ends of which are connected in common to the operating piston or rod. These interconnecting levers are relatively long; and in all of these devices, a relatively long stroke of the operating piston or rod is necessary to effect the cutting action for a relatively short distance of movement of the cutting blades. In addition, substantial pressure is applied to the intermediate pivot points of the interconnected rods and these intermediate pivot points move a relatively wide distance toward and away from the axis of the operating piston or rod.
Another group of patents which is comparable in many ways to the devices disclosed in the Baird, Carter, Parhaniemi, and Lind patents are the power driven or hydraulic shears and pliers disclosed in the patents to Cartwright U.S. Pat. No. 1,275,659; Bidin U.S. Pat. No. 2,791,028; Van Schaik U.S. Pat. No. 3,706,245; and Jahnke U.S. Pat. No, 3,893,237. None of these patents are directed to hoof nippers and all of the devices require a rather substantial axial movement of the operating piston or cylinder to accomplish a relatively limited movement between open and closed position of the cutting blades.
It is desirable to provide a sturdy, light-weight, easily manipulated power hoof trimmer or hoof nipper which overcomes the disadvantages of the prior art devices listed above. In addition, it is desirable to provide such a hoof nipper with adjustable and replaceable blades to prolong the usefulness of the operating life of the tool.